Investments (Amortized Cost and Fair Value of Fixed Maturities by Contractual Maturities) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Available for Sale Amortized Cost
Due in one year or less	$ 297,021
Due after one year through five years	786,836
Due after five years through ten years	475,749
Due after ten years	392,853
Total	2,495,928	2,609,253
Available for Sale Securities Fair Value
Due in one year or less	300,763
Due after one year through five years	842,063
Due after five years through ten years	521,609
Due after ten years	460,645
Total	2,693,323	2,800,593
Residential Mortgage Backed Securities [Member]
Available for Sale Amortized Cost
Debt Maturities, without single maturity date	119,382
Available for Sale Securities Fair Value
Debt Maturities, without Single Maturity Date	126,648
Commercial Mortgage Backed Securities [Member]
Available for Sale Amortized Cost
Debt Maturities, without single maturity date	276,142
Available for Sale Securities Fair Value
Debt Maturities, without Single Maturity Date	288,823
Asset-backed Securities [Member]
Available for Sale Amortized Cost
Debt Maturities, without single maturity date	147,945
Available for Sale Securities Fair Value
Debt Maturities, without Single Maturity Date	$ 152,772

This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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Amount after adjustments of available-for-sale debt securities at cost, maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount after adjustments of available-for-sale debt securities at cost, maturing after the tenth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing after the tenth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount after adjustments of available-for-sale debt securities at cost, maturing in the next fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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